Hot-melt adhesive having improved bonding strength

ABSTRACT

Hot-melt, pressure-sensitive adhesive compositions of amorphous polyalphaolefin and crystalline polypropylene have improved bond strength over the amorphous polyalphaolefin alone. The adhesive compositions improve dynamic shear strength, dynamic peel strength, as well as static peel strength. The adhesive compositions are particularly suitable for use in absorbent articles.

BACKGROUND OF THE INVENTION

[0001] People rely on disposable absorbent articles to make their liveseasier. Disposable absorbent articles, such as adult incontinencearticles and diapers, are generally manufactured by combining severalcomponents. These components typically include a liquid-permeabletopsheet; a liquid-impermeable backsheet attached to the topsheet; andan absorbent core located between the topsheet and the backsheet. Whenthe disposable article is worn, the liquid-permeable topsheet ispositioned next to the body of the wearer. The topsheet allows passageof bodily fluids into the absorbent core. The liquid-impermeablebacksheet helps prevent leakage of fluids held in the absorbent core.The absorbent core generally is designed to have desirable physicalproperties, e.g. a high absorbent capacity and high absorption rate, sothat bodily fluids can be transported from the skin of the wearer intothe disposable absorbent article.

[0002] Frequently one or more components of a disposable absorbentarticle are adhesively bonded together. For example, adhesives have beenused to bond individual layers of the absorbent article, such as thetopsheet (also known as, for example, the body-side liner) and backsheet(also known as, for example, the outer cover), together. Adhesives havealso been used to bond discrete pieces, such as fasteners and legelastics, to the article. In many cases, the bonding together ofcomponents forms a laminated structure in which adhesive is sandwichedbetween materials (such as layers of polymer film and/or layers of wovenor nonwoven fabrics) that make up the components being bonded together.

[0003] In many instances, a hot-melt adhesive, i.e. a polymericformulation that is heated to substantially liquefy the formulationprior to application to one or both materials when making a laminate, isused in making a laminated structure. While such formulations generallywork, they can be costly and their performance properties can beimproved. For example, adhesion can be improved to help provide asturdier laminate (e.g., to improve the integrity or strength of thebond between two components in a disposable absorbent article).

[0004] There is a need or desire for an adhesive composition thatpossesses one or more performance characteristics that are comparableto, or better than, one or more of the same performance characteristics(e.g., bond strength) of a conventional hot-melt adhesive and that willtypically cost less than a conventional hot-melt adhesive. Laminatedstructures and disposable absorbent articles employing the adhesivecomposition would benefit from these improved characteristics. There isalso a need or desire for efficient methods of making the adhesivecomposition, and efficient methods of making laminated structures anddisposable absorbent articles employing the adhesive composition.

SUMMARY OF THE INVENTION

[0005] The present invention is generally directed to amorphouspolyalphaolefin adhesive compositions having improved bonding strengththrough the addition of crystalline polypropylene. The adhesivecompositions have better performance characteristics, e.g. shear andpeel bonding strengths, than conventional hot-melt adhesives, and maycost less than conventional hot-melt adhesives.

[0006] The combination of amorphous polyalphaolefin (APAO) andcrystalline polypropylene possesses desirable adhesive properties andmay be used to make laminated structures and disposable absorbentarticles. The adhesive compositions of the invention can be applied to awide variety of substrates, including nonwoven webs, woven webs, andfilms. The adhesive can be applied in a swirl pattern, can bemelt-blown, or can be applied using any technique suitable for hot-meltadhesives.

[0007] Without being bound to any particular theory, it appears thatsuch a great difference between bonding strength of the adhesivecompositions of the invention and conventional amorphous polyalphaolefinadhesives may be attributed to crystallization of crystalline, orisotactic, polypropylene, which generates physical intermolecularlinking in the matrix of APAO.

[0008] As stated above, a material comprising a combination of an APAOand crystalline polypropylene may cost less than a conventional hot-meltadhesive. Generally this is because conventional hot-melt adhesives aretypically formulated by combining several components, including apolymer or polymers for cohesive strength; resins, tackifiers, or othergenerally low molecular-weight materials for adhesive strength;viscosity modifiers such as oils or wax-like materials; and otheradditives (e.g., antioxidants). In some versions of the invention, acombination of the APAO and crystalline polypropylene alone providesimproved bond characteristics compared to conventional hot-meltadhesives. But it should be understood that the invention encompassesadhesive compositions that include selected amorphous polyalphaolefinsand crystalline polypropylenes, combined with other additives ormaterials.

[0009] Another advantage present in some versions of the invention isthat the material of the invention may be used in conventionalhot-melt-adhesive processing equipment. Thus, the adhesive material maybe used in equipment already installed for the purpose of processing andapplying conventional hot-melt adhesives.

[0010] Apart from whether or not adhesive compositions of the presentinvention cost less than conventional hot-melt adhesives, we have foundthat representative embodiments of the present invention possessimproved performance characteristics compared to the performancecharacteristics of conventional hot-melt adhesives. These performancebenefits may justify processing and applying adhesive compositions ofthe present invention in modified conventional-hot-melt-adhesiveequipment, or in equipment especially designed and built for the purposeof processing and applying adhesive compositions of the presentinvention. Furthermore, these performance benefits may justify adhesivecompositions of the present invention, in some instances, being at ahigher cost than conventional-hot-melt adhesives.

[0011] These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 gives symbolic representations of syndiotactic, isotactic,and atactic configurations of a polymer.

[0013]FIG. 2 gives a visual representation of a fringed-micelle model ofa material having both amorphous and crystalline regions.

[0014]FIG. 3 shows a schematic diagram of one version of a method andapparatus for preparing, processing, and delivering an adhesivecomposition.

[0015]FIG. 4A shows one version of a feedback control scheme.

[0016]FIG. 4B shows one version of a feedforward control scheme.

[0017]FIG. 5 shows one version of a process control system.

[0018]FIG. 6 shows one version of a process for making a laminatecomprising an adhesive composition.

[0019]FIG. 7A shows a top view of a portion of one version of alaminate.

[0020]FIG. 7B shows a sectional, perspective view of a test panel cutfrom one version of a laminate.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0021] The present invention is generally directed to adhesivecompositions comprising amorphous polyalphaolefin (APAO) and crystallinepolypropylene. Adhesive compositions of the present invention generallyperform better, and typically cost less, than conventional hot-meltadhesives. Furthermore, these compositions may typically be processedand applied using conventional hot-melt adhesive processing equipment.Generally new equipment will not be necessary to use adhesivecompositions of the present invention.

[0022] Before describing representative embodiments of the invention, itis useful to define a number of terms for purposes of this application.These definitions are provided to assist the reader of this document.

[0023] “Nonwoven” fabric or web means a web having a structure ofindividual fibers or threads that are interlaid, but not in a regular oridentifiable manner as in a knitted fabric. Nonwoven fabrics or webshave been formed from many processes such as, for example, meltblowingprocesses, spunbonding processes, air laying processes, and bondedcarded web processes. The basis weight of nonwoven fabrics is usuallyexpressed in ounces of material per square yard (osy) or grams persquare meter (gsm) and the fiber diameters are usually expressed inmicrons. (Note: to convert from osy to gsm, multiply osy by 33.91.)

[0024] “Woven” fabric or web means a fabric or web containing astructure of fibers, filaments, or yams, which are arranged in anorderly, inter-engaged fashion. Woven fabrics typically containinter-engaged fibers in a “warp” and “fill” direction. The warpdirection corresponds to the length of the fabric while the filldirection corresponds to the width of the fabric. Woven fabrics can bemade, for example, on a variety of looms including, but not limited to,shuttle looms, rapier looms, projectile looms, air jet looms, and waterjet looms.

[0025] “Spunbonded fibers”, or “spundbond fibers”, means small-diameterfibers that are typically formed by extruding molten thermoplasticmaterial as filaments from a plurality of fine capillaries of aspinneret having a circular or other configuration, with the diameter ofthe extruded filaments then being rapidly reduced as by, for example, inU.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 toDorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat.Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 toHartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No.3,542,615 to Dobo et al., each of which is incorporated by reference inits entirety and in a manner consistent with the present document.Spunbond fibers are quenched and generally not tacky when they aredeposited onto a collecting surface. Spunbond fibers are generallycontinuous and often have average diameters larger than about 7 microns,and more particularly between about 10 and 30 microns. A spunbondmaterial, layer, or substrate comprises spunbonded (or spunbond) fibers.

[0026] The term “meltblown fibers” means fibers formed by extruding amolten material, typically thermoplastic in nature, through a pluralityof fine, usually circular, die capillaries as molten threads orfilaments into converging high-velocity heated gas (e.g., air) streamsthat attenuate the filaments of molten material to reduce theirdiameter, which may be to microfiber diameter. Thereafter, the meltblownfibers are carried by the high-velocity gas stream and are deposited ona collecting surface to form a web of randomly dispersed meltblownfibers. Such a process is disclosed for example, in U.S. Pat. No.3,849,241 to Butin. Meltblown fibers are microfibers which may becontinuous or discontinuous, are generally smaller than 10 microns indiameter, and are generally self-bonding when deposited onto acollecting surface.

[0027] As used herein, the term “microfibers” means small-diameterfibers having an average diameter not greater than about 100 microns,for example, having a diameter of from about 0.5 microns to about 50microns, more specifically microfibers may also have an average diameterof from about 1 micron to about 20 microns. Microfibers having anaverage diameter of about 3 microns or less are commonly referred to asultra-fine microfibers. A description of an exemplary process of makingultra-fine microfibers may be found in, for example, U.S. Pat. No.5,213,881, entitled “A Nonwoven Web With Improved Barrier Properties”.

[0028] “Amorphous polyalphaolefin” refers to a polymer that can includerandom copolymers or terpolymers of ethylene, propylene, and butene, andother substantially amorphous or semi-crystalline propylene-ethylenepolymers. Suitably, the amorphous polyalphaolefin (APAO) includesbetween about 20% and about 80% copolymers or terpolymers and betweenabout 20% and about 80% other substantially amorphous orsemi-crystalline propylene-ethylene polymers. Alternatively the APAOincludes between about 30% and about 70% copolymers or terpolymers andbetween about 30% and about 70% other substantially amorphous orsemi-crystalline propylene-ethylene polymers. As yet anotheralternative, the APAO includes between about 40% and about 60%copolymers or terpolymers and between about 40% and about 60% othersubstantially amorphous or semi-crystalline propylene-ethylene polymers.

[0029] “Crystalline polypropylene” refers to certain homopolymerpolypropylenes having at least 40% crystallinity, as well as certainpolypropylene copolymers having at least 40% crystallinity.

[0030] “Conventional hot-melt adhesive” means a formulation thatgenerally comprises several components. These components typicallyinclude one or more polymers to provide cohesive strength (e.g.,aliphatic polyolefins such as poly (ethylene-co-propylene) copolymer;ethylene vinyl acetate copolymers; styrenebutadiene or styrene-isopreneblock copolymers; etc.); a resin or analogous material (sometimes calleda tackifier) to provide adhesive strength (e.g., hydrocarbons distilledfrom petroleum distillates; rosins and/or rosin esters; terpenesderived, for example, from wood or citrus, etc.); perhaps waxes,plasticizers or other materials to modify viscosity (i.e., flowability)(examples of such materials include, but are not limited to, mineraloil, polybutene, paraffin oils, ester oils, and the like); and/or otheradditives including, but not limited to, antioxidants or otherstabilizers. A typical hot-melt adhesive formulation might contain fromabout 15 to about 35 weight percent cohesive strength polymer orpolymers; from about 50 to about 65 weight percent resin or othertackifier or tackifiers; from more than zero to about 30 weight percentplasticizer or other viscosity modifier; and optionally less than about1 weight percent stabilizer or other additive. It should be understoodthat other adhesive formulations comprising different weight percentagesof these components are possible.

[0031] While certain versions of the present invention encompasscombinations of an APAO and crystalline polypropylene only, it should beunderstood that other embodiments of the present invention comprisecomponents in addition to combinations of APAO and crystallinepolypropylene.

[0032] “Hot-melt processable” means that an adhesive composition may beliquefied using a hot-melt tank (i.e., a system in which the compositionis heated so that it is substantially in liquid form) and transportedvia a pump (e.g., a gear pump or positive-displacement pump) from thetank to the point of application proximate a substrate or othermaterial; or to another tank, system, or unit operation (e.g., aseparate system, which may include an additional pump or pumps, fordelivering the adhesive to the point of application). Hot-melt tanksused to substantially liquefy a hot-melt adhesive typically operate in arange from about 100 degrees Fahrenheit to about 450 degrees Fahrenheit.Generally, at the point of application, the substantially liquefiedadhesive composition will pass through a nozzle or bank of nozzles, butmay pass through some other mechanical element such as a slot. Ahot-melt processable adhesive composition is to be contrasted with acomposition that requires a conventional extruder, and the attendantpressures and temperatures characteristic of an extruder, to liquefy,mix, and/or convey the composition. While a hot-melt tank and pump in ahot-melt processing system can handle adhesive-composition viscositiesin a range from about 1000 centipoise to about 10,000 centipoise, anextruder can handle and process adhesive-composition viscosities in arange from about 10,000 centipoise to viscosities of several hundredthousand centipoise. An advantage of some adhesive compositions of thepresent invention is that the compositions are hot-melt processable;i.e., the combination of APAO and crystalline polypropylene may besubstantially liquefied in a hot-melt tank and conveyed to the point ofapplication via a pump. As was stated above, however, some adhesivecompositions of the present invention may not possess this particularadvantage.

[0033] Unless otherwise noted, “Laminated structure” or “laminate” meansa structure in which one layer, material, component, web, or substrateis adhesively bonded, at least in part, to another layer, material,component, web, or substrate. As stated elsewhere in this application, alayer, material, component, web, or substrate may be folded over andadhesively bonded to itself to form a “laminated structure” or“laminate.”

[0034] “Polymer”, as used herein, generally includes, but is not limitedto, homopolymers, copolymers, such as, for example, block, graft, randomand alternating copolymers, terpolymers, and blends and modificationsthereof. As is explained in this document, polymers may assume differentconfigurations, including isotactic, atactic, and syndiotacticconfigurations. “Configuration” describes those arrangements of atomsthat cannot be altered except by breaking and reforming primary chemicalbonds (i.e., covalent bonds). In contrast, “conformation” describesarrangements that can be altered by rotating groups of atoms aroundsingle bonds. It should be noted that a single polymer chain may besynthesized such that some portions of the chain have an isotacticconfiguration and some portions of the chain have an atacticconfiguration.

[0035] A graphic example provides additional detail on the types ofconfigurations mentioned above. If a polymer chain is depicted in afully-extended, planar, zigzag conformation 1100, the configurationresulting when all the substituent groups R 1102 on the polymer lieabove (depicted in FIG. 1B) or below (not depicted) the plane of themain chain is called “isotactic”. If substituent groups lie alternatelyabove and below the plane the configuration is called “syndiotactic”(depicted in FIG. 1A). And a random sequence of substituents lying aboveand below the plane is described as an “atactic” configuration (depictedin FIG. 1C). A polymer, or a region of a polymer, having an isotacticconfiguration is more likely to assume characteristics of a crystallinestructure. Pure isotactic polymers are rare. For purposes of thisinvention, the term “isotactic polymer” refers to a polymer that is atleast 60% isotactic, suitably at least 70% isotactic, alternatively atleast 80% isotactic. A polymer, or a region of a polymer, having anatactic configuration is more likely to assume characteristics of anamorphous structure. An atactic polymer may assume some crystallinity,but the degree of crystallinity is typically less than 20%, or less than15%. For purposes of this invention, the term “atactic polymer” refersto a polymer that may not be 100% atactic, but is at least 90% atactic.Similarly, for the purposes of this invention, the term “amorphouspolymer” may assume some crystallinity, but the degree of crystallinityis typically less than 20% or less than 15%. And a polymer, or a regionof a polymer, having a syndiotactic configuration can assumecharacteristics of a crystalline structure, but to a degree less thanthe degree of crystallinity in an isotactic configuration.

[0036] In this application, “fringed-micelle model” means a theoreticalconstruct characterizing polymeric structures that have both crystalline150 and amorphous 152 regions (one version of a graphic depiction of afringed-micellar structure is presented in FIG. 2). This model may beused to characterize the structure of an atactic polymer and anisotactic polymer individually, i.e., each polymer possesses bothcrystalline regions and amorphous regions. As explained above, theisotactic polymer likely possesses a greater degree of crystallinitycompared to an atactic polymer. Furthermore, this model may be used tocharacterize the structure of a blend of isotactic polymer and atacticpolymer. It should be understood that this model provides one possibleview of characteristics of the present invention and in no way limitsthe scope thereof.

[0037] One version of an adhesive composition possessing features of thepresent invention comprises an APAO, such as a butene-1 copolymer withethylene or propylene, or a butene-1 terpolymer with ethylene andpropylene, having a number-average molecular weight of from about 5,000to about 30,000, specifically about 10,000 to about 20,000. The butene-1copolymer should include about 20% to about 65% by weight butene-1, orabout 30% to about 55% by weight butene-1, and a balance of thecomonomer or comonomers. Alternatively, the APAO may include anethylene-propylene copolymer having up to 80% ethylene. An example of acommercially available APAO suitable for use in the invention is REXTAC®2730, or RT 2730, available from Huntsman Corporation, Salt Lake City,Utah.

[0038] The composition also includes crystalline polypropylene having adegree of crystallinity of about 40% or more, specifically of about 60%or more, particularly of about 80% or more, and a number-averagemolecular weight of from about 3000 to about 200,000, more particularlyof about 10,000 to about 100,000. An example of a commercially availablecrystalline polypropylene suitable for use in the invention is isotacticpolypropylene, available from Sigma-Aldrich. The crystallinepolypropylene may also include syndiotactic polypropylene, orcombinations of isotactic and syndiotactic polypropylene. The adhesivecomposition is hot-melt processable at a temperature of about 450degrees Fahrenheit or less, specifically at a temperature of about 400degrees Fahrenheit or less, particularly at a temperature of about 375degrees Fahrenheit or less, and suitably at a temperature of about 350degrees Fahrenheit or less.

[0039] This adhesive composition can have a melt index between about 200and about 2000 grams per 10 minutes, or between about 400 and about 1800grams per 10 minutes, or between about 500 and about 1500 grams per 10minutes, as determined using ASTM D 1238, 230° C./2.16 kg Method. Themelt index is dependent upon the crystallinity, molecular weight, andthe molecular weight distribution of the polymers included in theadhesive composition.

[0040] In some versions of the invention, the APAO is present in anamount of about 70 to about 90 weight percent and the crystallinepolypropylene is present in an amount of about 10 to about 30 weightpercent. In another embodiment of the invention, the APAO is present inan amount of about 73 to about 87 weight percent and the crystallinepolypropylene is present in an amount of about 13 to about 27 weightpercent. In yet another embodiment of the invention, the APAO is presentin an amount of about 75 to about 85 weight percent and the crystallinepolypropylene is present in an amount of about 15 to about 25 weightpercent. For purposes of this invention, weight percent is defined asthe mass of one type of polymer (e.g., APAO) in the adhesive compositiondivided by the sum of the masses of other types of polymer (e.g., APAOand crystalline polypropylene) in the adhesive composition, plus themass(es) of any additional component(s) that might be present in theadhesive composition, with this value being multiplied by 100. So, forexample, if we form an adhesive composition comprising 80 grams of APAOwith 20 grams of crystalline polypropylene, the combination includes 80weight percent APAO.

[0041] In another aspect, the invention encompasses laminated structuresemploying embodiments of the adhesive composition as described above.For example, one version of a laminated structure of the presentinvention comprises a first layer and a second layer, wherein at least aportion of the first layer is attached to at least a portion of thesecond layer using an adhesive composition that is the same as, oranalogous to, one or more of the embodiments described above, andwherein the laminated structure has improved dynamic peel strength,improved dynamic shear strength, and improved static-peel-failure time,relative to conventional hot-melt adhesive compositions.

[0042] For any of the laminated structures described above, the firstand second layer may be part of one-and-the-same substrate. That is, thesubstrate may be folded over and joined to itself using an adhesivecomposition of the present invention.

[0043] Furthermore, the first layer, second layer, or both may comprisea variety of materials, including, but not limited to a nonwoven (e.g.,a necked-bonded laminate or a spun-bond material); a film; a wovenmaterial; a substrate comprising cellulosic material, thermoplasticmaterial, or both; some combination of these; or the like.

[0044] In yet another aspect, an absorbent article may be formed thatemploys an adhesive composition of the present invention and/or alaminated structure of the present invention. So, for example, oneversion of an absorbent article of the present invention comprises aliquid-permeable topsheet; a liquid-impermeable backsheet; and alaminated structure having features of the present invention, such asone or more of the versions described above. Some or all of thebacksheet may include the laminated structure; some or all of thetopsheet may include the laminated structure; the laminated structuremay be attached, directly or indirectly, to the backsheet, the topsheet,or both; or a laminated structure or structures may be present in somecombination of these.

[0045] In addition to various versions of adhesive compositions,laminated structures, and absorbent products of the present invention,the present invention also encompasses methods of making thesecompositions, structures, and articles of manufacture.

[0046] One version of a method of making a laminated structure havingfeatures of the present invention comprises the steps of providing afirst substrate; providing a second substrate; providing an APAO havinga weight-average molecular weight of from about 20,000 to about 60,000,specifically about 25,000 to about 50,000; and providing an isotacticpolypropylene, namely a crystalline polypropylene having a degree ofcrystallinity of about 40% or more, specifically of about 60% or more,particularly of about 80% or more, and a weight-average molecular weightof from about 20,000 to about 300,000, more particularly of about 35,000to about 200,000. The APAO and the crystalline polypropylene are heatedso that they are sufficiently liquefied for blending. The heated APAOand the heated crystalline polypropylene are blended to form an adhesivecomposition that is melt-processable at a temperature of less than about450 degrees Fahrenheit, specifically of less than about 400 degreesFahrenheit, particularly of less than about 375 degrees Fahrenheit, andsuitably of less than about 350 degrees Fahrenheit. The adhesivecomposition is applied to the first substrate, the second substrate, orboth substrates. At least a portion of the first substrate is joined toat least a portion of the second substrate so that some or all of theapplied adhesive composition is positioned between the first substrateand second substrate.

[0047] In some methods of the present invention, the APAO is present inan amount of about 70 to about 90 weight percent and the crystallinepolypropylene is present in an amount of about 10 to about 30 weightpercent. In other methods of the invention, the APAO is present in anamount of about 73 to about 87 weight percent and the crystallinepolypropylene is present in an amount of about 13 to about 27 weightpercent. In still other embodiments of the invention, the APAO ispresent in an amount of about 75 to about 85 weight percent and thecrystalline polypropylene is present in an amount of about 15 to about25 weight percent.

[0048] It should be understood that the APAO and crystallinepolypropylene could be heated and blended at a site other than the sitewhere the laminate is being formed. For example, APAO and crystallinepolypropylene could be blended using an extruder/sigma blade mixer orhot-melt processing equipment at a first geographic location. The blendcould then be allowed to cool and processed to make a solid form (e.g.,block or brick). The APAO/crystalline polypropylene blend, in solidform, could then be shipped from the first geographic site to a sitewhere a laminate is to be made. The blend, in solid form, would simplybe heated to substantially liquefy the adhesive composition prior to itsbeing used to make a laminate.

[0049] It should also be understood that a method having features of thepresent invention encompasses different sequences of steps by which theadhesive composition is made. For example, the APAO could be heated in afirst container. The crystalline polypropylene could be heated in asecond container, before, after, or concurrently with the heating of theAPAO. Then, the two substantially liquefied polymers could be blended inthe first container, the second container, or a third container.Alternatively, one of an APAO or crystalline polypropylene could beheated in a container, and after the selected polymer is substantiallyliquefied, the remaining polymer could be added to the same container tobe heated and blended. In another alternative, the APAO and crystallinepolypropylene could be added to the same container to be heated andblended at the same time. In other words, our invention contemplatesvarious methods and sequences by which selected amounts of APAO andcrystalline polypropylene (plus any other optional additives) are heatedand blended to form an adhesive composition of the present invention.

[0050] The preceding discussion assumes that the APAO and crystallinepolypropylene are in substantially solid form at room temperature, ortemperatures that are typically present in a working environmentsuitable for human beings. To the extent that the APAO or crystallinepolypropylene is available in substantially liquid form, then thosesteps providing for heating and liquefying that material (i.e., thealready-liquefied material) can be omitted from methods of the presentinvention.

[0051] A method of making an adhesive composition having features of thepresent invention comprises the steps of providing an APAO having aweight-average molecular weight of from about 20,000 to about 60,000,specifically about 25,000 to about 50,000, and providing an isotacticpolypropylene, namely a crystalline polypropylene having a degree ofcrystallinity of about 40% or more, specifically of about 60% or more,particularly of about 80% or more, and a number-average molecular weightof from about 3000 to about 200,000, more particularly of about 10,000to about 100,000. The APAO and the crystalline polypropylene are heatedso that they are sufficiently liquefied for blending. The heated APAOand the heated crystalline polypropylene are blended to form an adhesivecomposition that is melt-processable at a temperature of less than about450 degrees Fahrenheit, specifically of less than about 400 degreesFahrenheit, particularly of less than about 375 degrees Fahrenheit, andsuitably of less than about 350 degrees Fahrenheit.

[0052] In some methods of the present invention, the APAO is present inan amount of about 70 to about 90 weight percent and the crystallinepolypropylene is present in an amount of about 10 to about 30 weightpercent. In other methods of the invention, the APAO is present in anamount of about 73 to about 87 weight percent and the crystallinepolypropylene is present in an amount of about 13 to about 27 weightpercent. In still other embodiments of the invention, the APAO ispresent in an amount of about 75 to about 85 weight percent and thecrystalline polypropylene is present in an amount of about 15 to about25 weight percent.

[0053] One version of a method in which an adhesive composition of thepresent invention is metered or delivered at a desired rate to a unitoperation (e.g., a unit operation where the adhesive composition isapplied to a substrate or substrates in order to make a laminate)comprises the steps of: determining the amount of adhesive compositionbeing used by the unit operation per unit time; and forceadjusting thevolumetric flow rate or the mass flow rate of the adhesive compositionso that the amount of adhesive composition being metered or delivered tothe unit operation corresponds to the amount of adhesive compositionbeing used by the unit operation per unit time.

[0054] In the process description that follows, the preparation,processing, and application of an adhesive composition including APAOand crystalline polypropylene is described. It should be understood,however, that this description is given as an example. Other processingmethods and equipment may be used to prepare and deliver variousadhesive compositions of the present invention.

[0055]FIG. 3 shows a schematic diagram of an apparatus 20, and a methodfor spraying an adhesive composition, on a moving web 22. The apparatus20 may include a programmable control system 24 that is operativelyconnected to a flow-control system 26. The combination of theprogrammable control system 24 and the flow-control system 26 areconfigured to control the delivery of an adhesive composition in liquidform to the moving web 22. Generally an adhesive composition is receivedin solid form at a manufacturing site where equipment such as thatdepicted in FIG. 3 is located. For example, hot-melt adhesivecompositions may be received as solid pellets, blocks, or some othershape. The solid is then heated so that the hot-melt adhesivecomposition is in a form such that it can be conveyed, and applied, to asubstrate or other material. Usually this requires that the heatedhot-melt adhesive be in substantially liquid form. For the presentinvention, an adhesive composition comprising an APAO and crystallinepolypropylene (e.g., butene-1 copolymer and crystalline polypropylene),in solid form, might be received at a manufacturing site for heating andprocessing as described above. Alternatively, the APAO and crystallinepolypropylene might be received as separate components to be blended atthe manufacturing site. As discussed above, the present inventionencompasses a variety of sequences of steps for making adhesivecompositions of the present invention. An example of equipment andmethods for heating an adhesive composition, or precursor materials tothe adhesive composition, are described in more detail below.

[0056] The apparatus may also include a position-sensing system that isconfigured to sense a position of the moving web 22 and, in responsethereto, generate a signal that is sent to the programmable controlsystem 24.

[0057] As representatively illustrated in FIG. 3, the continuouslymoving web 22 may be supplied by any means known to those skilled in theart, such as known conveyor systems. The continuously moving web 22 caninclude any type of layer or web of material, such as films, nonwovenwebs, woven webs which may include strands of thermoplastic material;natural material such as threads of cotton and the like, laminatematerials, or combinations thereof. More particularly, the continuouslymoving web 22 may include a necked-bonded laminate (“NBL”), whichgenerally comprises a polyethylene layer sandwiched between twopolypropylene, spunbonded layers; a polypropylene, spunbonded layer(“SB”); or an outercover comprising a polyethylene layer and apolypropylene, spunbonded layer. For additional detail on how NBLs andother neck-bonded materials are formed, see U.S. Pat. No. 5,336,545 toMorman, entitled “Composite Elastic Necked-Bonded Material,” which ishereby incorporated by reference in its entirety in a manner consistentwith the present document.

[0058] As is described below in more specific terms, the adhesive issprayed on the continuously moving web 22 in a specific design orpattern for subsequent placement of or bonding to another material. Theother material can be the same or different than the web to whichadhesive was applied. In some cases adhesive might be applied to bothsubstrates before they are joined together. And, as mentioned above, onesubstrate might be folded over and attached to itself to form alaminated structure.

[0059] The programmable control system 24 of the present invention isconfigured to send signals to the flow control system 26 which, inresponse thereto, is configured to initiate a spray of adhesive at thecorrect time to provide the desired pattern of adhesive on the movingweb 22. As representatively illustrated in FIG. 3, the flow controlsystem 26 includes an adhesive source 28 which is configured to deliveran adhesive through an adhesive supply line 30 to a metering mechanism32. The adhesive can be delivered to the metering mechanism 32 by anymeans known to those skilled in the art, such as by the use of a pump.

[0060] The metering mechanism 32 is configured to continuously supply atleast one independent, volumetric flow of adhesive to a respectivenozzle. As used herein, the term “volumetric flow” refers to a flow ofadhesive that has a predetermined volumetric flow rate. Such a“volumetric flow” may be provided by a positive-displacement meteringpump which is configured to supply a specific volumetric flow which isindependent of the manner in which the adhesive is supplied to themetering mechanism 32. As a result, for an adhesive that is at a givendensity, the metering mechanism 32 is configured to provide anindependent, predetermined mass flow rate of adhesive to each nozzle.Other adhesive processing and delivery systems utilize pressure toprovide a flow of adhesive.

[0061] The metering mechanism 32 of the present invention may beconfigured to supply a single, volumetric flow of adhesive to one nozzleor an independent, volumetric flow of adhesive to each of a plurality ofnozzles depending upon the number of nozzles required to provide thedesired pattern of adhesive on the moving web 22. A suitable device toprovide the metering mechanism 32 may include a positive-displacementmetering pump which is commercially available from May CoatingTechnologies, Acumeter Division, a business having offices located inHolliston, Mass., under the trade designation No. 19539. The meteringmechanism 32 may include any other piston pump or gear pump which arewell known to those skilled in the art.

[0062] The metering mechanism 32 may be configured to supply any desiredvolumetric flow rate of adhesive to each nozzle. For example, themetering mechanism 32 may be configured to provide a pre-determinedvolumetric flow rate of from about 1 to about 1000 cubic centimeters perminute and suitably from about 30 to about 180 cubic centimeters ofadhesive per minute to each nozzle. The metering mechanism 32 may beconfigured to provide either a constant or a variable volumetric flowrate of adhesive to each nozzle. For example, if the metering mechanism32 is a positive-displacement metering pump, the speed of the pump maybe controlled to vary the volumetric flow rate of adhesive to thenozzles.

[0063] Each nozzle 38 and 40 as representatively illustrated in FIG. 3can be any device which is capable of providing the desired pattern ofadhesive on the moving web 22. For example, one suitable nozzle iscommercially available from Nordson Corporation, a business havingoffices located in Duluth, Ga., under the trade designation Model No.144906. Another suitable nozzle for use in the present invention isobtainable from ITW Dynatec Co. of Hendersonville, Tenn., under thetrade designation number 057B1639,1.D. #A3. Such nozzles are typicallyconfigured to be operated between an on position and an off position tocontrol the spray of adhesive from the nozzles. When operated in the onposition, each nozzle may be configured to spray substantially theentire volumetric flow of adhesive which is independently supplied to itto more accurately control the amount and pattern of the adhesive on themoving web. The nozzles 38 and 40 may further be configured to includeair streams that can be directed to provide a desired pattern in thespray of adhesive being dispensed from each nozzle. Such air streams canprovide a desired adhesive spray pattern, such as a pattern of swirls ofadhesive. The adhesive can be applied to the moving web 22 in aconcentration of between about 1 gram per square meter (gsm) and about50 gsm, or between about 5 gsm and about 20 gsm.

[0064] After the pattern of adhesive has been sprayed on the moving web22, the web may be further processed in a variety of ways. For example,the continuously moving web 22 may be contacted by a second substrateweb, such as a nonwoven layer, between a pair of nip rolls to adhesivelyjoin the two substrate webs together. Thereafter, this compositematerial or laminate may be used in a variety of ways such as in theconstruction of disposable absorbent articles such as diapers,incontinent articles, training pants, feminine care articles and thelike.

[0065] The above discussion provides one example of hot-melt processingequipment 15 and a system for applying adhesive to a substrate. Itshould be understood that this is but one example, and that the presentinvention encompasses other systems for preparing and applying adhesives(see, e.g., U.S. Pat. No. 4,949,668, entitled “Apparatus for SprayedAdhesive Diaper Construction,” which issued on Aug. 21, 1990, and whichis hereby incorporated by reference in its entirety and in a mannerconsistent with the present document).

[0066] Regardless of the system used to apply the adhesive, theresulting composite material or laminate may be exposed to thermal,infrared, ultrasonic, or other forms of energy in subsequent unitoperations or processing steps. For example, the laminate or compositematerial may pass through an ultrasonic-bonding unit operation whereinthe laminate or composite material are exposed to ultrasonic energy.After exemplary composite materials or laminates such as those referredto above are formed using an adhesive composition of the presentinvention, some or all of the composite or laminate may be exposed toultrasonic energy. Referring to PCT International Publication Number WO99/25296, which is hereby incorporated by reference in its entirety in amanner consistent with the present document, the publication disclosesthe use of ultrasonic bonding to form side seams or seals in thedisposable underpant. (See, e.g., page 29, lines 10-25; additionaldetail regarding the forming of such side seals is disclosed in U.S.Pat. No. 4,610,681, which issued on Sep. 09, 1986 and is entitled“Disposable Underpants Having Discrete Outer Seals,” and which is herebyincorporated by reference in a manner consistent herewith; and U.S. Pat.No. 4,641 ,381, which issued on Feb. 10, 1997 and is entitled“Disposable Underpants, Such as Infant's Training Pants and the Like,”which is also incorporated by reference in a manner consistent with thepresent document.)

[0067] Thus, adhesives of the present invention, used to make laminatesand composite materials, may be exposed to ultrasonic energy whenultrasonic-bonding equipment is used in subsequent processing steps(e.g., when the ultrasonic bonding equipment is used to form the seamsor seals in the disposable absorbent article as discussed above).

[0068] Specific examples of composite materials, laminates, anddisposable absorbent articles with which adhesives of the presentinvention may be utilized are disclosed in the following U.S. patentsand U.S. patent applications: U.S. Pat. No. 4,798,603 issued Jan.17,1989, to Meyer et al.; U.S. Pat. No. 5,176,668 issued Jan. 5, 1993, toBernadine; U.S. Pat. No. 5,176,672 issued Jan. 5, 1993, to Bruemmer etal; U.S. Pat. No. 5,192,606 issued Mar. 9, 1993, to Proxmire et al.;U.S. Pat. No. 4,940,464, entitled “Disposable Incontinence Garment orTraining Pant”; U.S. Pat. No. 5,904,675, entitled “Absorbent ArticleWith Improved Elastic Margins and Containment System”; U.S. Pat. No.5,904,672, entitled “Absorbent Article Having Improved Waist RegionDryness and Method of Manufacture”; and U.S. Pat. No. 5,902,297,entitled “Absorbent Article Having a Collection Conduit.” Each of thepreceding U.S. patents is incorporated by reference in its entirety andin a manner consistent with the present document. More specifically, thetypes of absorbent articles in which the adhesives of the presentinvention may be used include diapers, children's training pants, swimwear, incontinence products, feminine care products, other personal careor health care garments, including medical garments, or the like. Itshould be understood that the present invention is applicable to otherstructures, composites, or products incorporating adhesive compositionsof the present invention.

[0069] Additional Detail on Representative Process-Control Embodiments

[0070] As discussed above, process-control systems may be used tocontrol the volumetric or mass flow rate of adhesive compositions of thepresent invention to a point of application (e.g., to a point ofapplication on a substrate, layer, or web that will be used to make alaminate or composite material). Persons of ordinary skill in the art ofprocess control are familiar with the various process-controlstrategies, algorithms, and equipment used to control a process. Some ofthe possible strategies that may be used to control a process includefeedback-control strategies (i.e., a process in which a variable to becontrolled is measured, the measured value is compared to a desiredvalue, and the difference between the measured value and the desiredvalue is transmitted to a feedback controller that force adjusts amanipulative variable to drive the measured variable back to the desiredvalue) (see, e.g., FIG. 4A); feedforward-control strategies (i.e., aprocess in which a disturbance entering a process is detected, and anappropriate change is made to a manipulative variable so that an outputvariable is held constant; see, e.g., FIG. 4B); and the like.

[0071] One example of a process-control system is depicted in FIG. 5. Asensor may be used to determine a signal S₁ corresponding to thevariable to be controlled, e.g. the volumetric or mass flow rate ofadhesive being sprayed or delivered in an adhesive-application unitoperation 74. This signal may then be relayed electrically,pneumatically, hydraulically, or by other means to a transmitter 76,which converts the signal S₁ into a control signal M₁. The transmittertransmits the control signal M₁ to the controller 78.

[0072] After receiving the control signal M₁, the controller sends thecorresponding output signal R₁ to the control element 80. The controlelement, such as an electronic or pneumatic control valve, responds tothe output signal R₁ by opening or closing, thus effecting the desiredchange to the variable being manipulated, in this case the volumetric ormass flow rate of adhesive. Alternatively, the control element mighteffect a desired change to the speed at which a pump operates, therebycontrolling the mass or volumetric flow rate of adhesive.

[0073] As mentioned above, an air-pressure, electrical, pneumatic, orother signal may be used to transmit information (e.g., the varioussignals discussed in the preceding paragraphs) from one device toanother (e.g., from a sensor, to a transmitter, to a controller, to acontrol element, or to some combination of some or all of these). Forexample, the controller may be a device that converts a control signalinto an equivalent air-pressure, electrical, pneumatic, or other outputsignal. This air-pressure, electrical, pneumatic or other output signalis sent from the controller to a control element that effects a changeto the variable being manipulated. If the output signal is anair-pressure signal, the output signal will be transmitted to thecontrol element via tubing. The control element, such as a pneumaticcontrol valve, responds to the output signal by opening or closing, thuseffecting the desired change to the variable being manipulated. Thecontrol system may include multiple valves: e.g., a two-valve systemwith one operating as a one-directional, open-or-shut valve and theother operating as a proportional valve. Alternatively, the outputsignal is converted into an electrical signal. The output signal isrelayed to the control element via metal wire or other electricalconductor. The control element, such as an electronic control valve,responds to the electrical signal by opening or closing, thus effectingthe desired change to the variable being manipulated.

[0074] An operator may input a value directly to the controller toproduce a control signal. For example, an operator may adjust a dial orother input device on a pneumatic, hydraulic, electronic, or othercontroller to adjust the volumetric or mass flow rate of adhesive. Theoperator selects a setting on the input device of the controllercorresponding to the flow rate desired by the operator. Typically theoperator will have calibrated the input device on the controller so thatinput-device settings each correspond to specific volumetric or massflow rate values.

[0075] A general-purpose computer may be used in place of, or inaddition to, the controller mentioned above. Typically a general-purposecomputer employs an input device, including, but not limited to, analpha-numeric keyboard, mouse, joystick, stylus, touch screen, or somecombination of these. Other devices which may be used to input data tothe computer include, but are not limited to: devices for reading datastored on magnetic media such as 3.5 inch “floppy disks” orfixed-drives; devices for reading data stored on optical media, such asCD-ROMs; devices for reading data transmitted over cables, includingoptical cables; and devices for scanning and digitizing information on adocument. In addition to the input devices like those mentioned above, ageneral-purpose computer usually includes a visual display fordisplaying data. Also, a general-purpose computer typically has a devicefor storing and retrieving data that is inputted to the computer.Devices for storing and retrieving data include, but are not limited to:a disk drive for reading data from, and storing data on, a 3.5 inch“floppy disk”; a hard disk or other fixed drive; a tape drive; or otherdevice capable of reading data from, and storing data on, magneticmedia.

[0076] A general-purpose computer may be adapted for use in controllingthe volumetric or mass flow rate of adhesive. Typically ageneral-purpose computer comprises devices for data input, data storage,data processing, data display, and data output, as discussed above. Forpurposes of controlling volumetric or mass flow rate, thegeneral-purpose computer may further comprise a set of instructionscomprising the following steps: reading the control signal M₁, thecontrol signal M₁ being transmitted to the computer in computer-readableform; correlating the control signal M₁ to an output signal R₁ andtransmitting the output signal R₁ to a control element. The controlelement, such as an electronic, hydraulic, pneumatic, or other controlvalve, responds to the output signal R₁ by opening or closing, thuseffecting the desired change to the variable being manipulated, in thisvolumetric or mass flow rate. Alternatively, the control element mayeffect desired changes to the speed at which a positive-displacement orother metering pump operates, thereby effecting desired changes to massor volumetric flow rates.

[0077] The above discussion provides exemplars of equipment and methodsfor controlling the amount of adhesive being conducted to a point ofapplication per unit time. It should be understood that other equipmentand methods used to force adjust the flow rate of an adhesive of thepresent invention to a control set point, operatorinputted value, orother desired value falls within the scope of the present invention.

TESTS/PROCEDURES

[0078] Laminate Production

[0079] Laminates were made on equipment available from J & MLaboratories, a business having offices located in Dawsonville, Ga. Asdepicted in FIG. 6, a first substrate or first base material 102, suchas a nonwoven web, was directed from its corresponding unwind stand (notshown) to the surface of a 6-inch-diameter steel roll 104 and through anip 106 between the steel roll and a 4-inch-diameter rubber roll 110. Asecond substrate or second base material, such as a second nonwoven web108, was directed from its unwind stand (not shown) to the surface ofthe rubber roll and through the nip. Typically, the equipment wasoperated at a speed of 300 feet per minute.

[0080] The applicator 114 used to deposit the adhesive was positioned sothat the face of the depicted nozzle, which was roughly parallel to thesurface of the web to which adhesive was first applied, was 1.5 inches116 from the surface of the web. Furthermore, the central axis of thedepicted nozzle, which is perpendicular to the web to which adhesive isfirst applied, was 8 inches 118 from a parallel axis that passes throughthe nip defined by the rubber and steel rolls.

[0081] From the discussion above, it should be understood that thesubstrates and the resulting laminate 700 generally moved in a machinedirection 702 (see FIG. 7A) during their preparation. FIG. 7A depicts atop view of a portion of a laminate after it has been formed. Acontinuous band of adhesive 703, whether it was applied usingmeltblowing, cycloidal, slot, or other application technique, is denotedby broken lines 705 and 707. The adhesive is under the upper substrateof the laminate depicted in the Figure. As the laminate is made in acontinuous manner, it is wound up in the form of a roll. The directionthat is perpendicular to the machine direction, but lying within theplane of the laminate, is denoted as the cross-machine direction 704.Typically the width of the formed laminate, width denoting the dimensionparallel to the cross-machine direction, was about 4 inches 706. Thewidth of the applied adhesive, again width denoting a dimension parallelto the cross-machine direction, typically was from about 0.5 inches toabout 1 inch 708. Also, the band of adhesive was generally applied suchthat it was substantially centered in the laminate (in the widthdimension). Unless otherwise noted, the width of the applied adhesivewas about 0.5 inches. (Note: the lines 710 and 712 denote the manner inwhich a 2-inch 714 sample was cut for subsequent analysis; samplepreparation and orientation is discussed in more detail below).

[0082] The selected adhesive was either an adhesive of the presentinvention (as noted in the Examples below), or a hot-melt adhesive(again as noted in the Examples below). The adhesive was added using avariety of patterns, including a meltblown pattern, a swirl or cycloidalpattern, or a pattern resulting from slot coating. Typically theadhesives were heated to temperatures ranging from about 350 degreesFahrenheit to about 380 degrees Fahrenheit prior to application to oneof the substrates. Unless otherwise noted, the selected adhesive wasadded using a meltblown pattern. As stated above, unless otherwise notedthe width of the added adhesive was about 1.0 inch. The selectedadhesive was added in amounts varying from about 5 grams per squaremeter to about 30 grams per square meter, with specific applicationlevels or add-on levels noted in the examples.

[0083] A number of different substrates were used to prepare thelaminates, as noted in the Examples below. The substrates that were usedincluded: a necked-bonded laminate (“NBL”), which generally comprised apolyethylene layer sandwiched between two polypropylene, spunbondedlayers; a polypropylene, spunbonded layer (“SB”); and an outercover(“OC”) comprising a polyethylene layer and a polypropylene, spunbondedlayer. For tests where the performance of a laminate of the presentinvention was compared to the performance of a laminate prepared using aconventional hot-melt adhesive, the same substrates were used to prepareboth the laminate of the present invention and the conventionallaminate.

[0084] 180° Static Peel Test

[0085] The 180° static peel test was used to determine the approximatetime to failure of a laminate in which one substrate was adhesivelybonded to another substrate. All laminates were made as described aboveon a J & M machine. Samples were cut from the prepared laminate which,was in the form of a continuous web prepared on a J & M machine, asshown in FIG. 7A. FIG. 7B depicts a sectional view of a sample that hasbeen removed from the laminate depicted in FIG. 7A. The test procedurewas conducted as follows: 1. A 2-inch test panel was cut from thelaminate, as shown in FIGS. 7A and 7B. 2. The test laminate was thensuspended vertically in a forced-air oven, model number OV-490A-2manufactured by Blue M Co., a business having offices in Blue Island,Ill., that had been preheated to a temperature of 100 degreesFahrenheit, with the top of one substrate layer 750 secured by a clampor other mechanical securing element, the clamp or securing elementhaving a width greater than 2 inches. 3. A 500-gram weight was thenaffixed to the top edge 752 of the other substrate using a clamp orother mechanical securing element. Again, the clamp or securing elementused to attach the 500-gram weight was wider than 2 inches. 4.Approximately every ½ hour, the test laminate was visually examined byquickly opening the oven door. The time at which one substrate or layerhad detached from the other substrate or layer was recorded. Therecorded time corresponded to the approximate time of failure of thelaminate. The two, now separate, substrates were then examined todetermine the nature of the failure. If the substrates separated suchthat most of the adhesive remained on one of the substrates, thenfailure was deemed to be an adhesion failure (i.e., failure likelyoccurred at the interface between one of the substrates and the adhesivecomposition). If the substrates separated such that adhesive remained onboth substrates, the failure was deemed to be a cohesion failure (i.e.,separation likely occurred within the adhesive composition itself). Ifneither of these conditions arose, but instead one or both of thesubstrates failed (i.e., that portion of the laminate bonded by theadhesive, usually a 1.0 inch by 2 inch area of the test panel), then thefailure was deemed a material failure of one or both substrates.

[0086] Dynamic Peel and Shear Testing

[0087] To determine dynamic peel strength, a laminate was tested for themaximum amount of tensile force that was needed to pull apart the layersof the laminate. Values for peel strength were obtained using aspecified width of laminate (for the present application, 2 inches);clamp jaw width (for the present application, a width greater than 2inches); and a constant rate of extension (for the present application,a rate of extension of 300 millimeters per minute). For samples having afilm side, the film side of the specimen is covered with masking tape,or some other suitable material, in order to prevent the film fromripping apart during the test. The masking tape is on only one side ofthe laminate and so does not contribute to the peel strength of thesample. This test uses two clamps, each clamp having two jaws with eachjaw having a facing in contact with the sample, to hold the material inthe same plane, usually vertically. The sample size is 2 inches (10.2cm) wide by 4 inches (20.4 cm). The jaw facing size is 0.5 inch (1.25cm) high by at least 2 inches (10.2 cm) wide, and the constant rate ofextension is 300 mm/mm. For a dynamic peel test, one clamp is attachedto the top 750 of one substrate of a test panel (see FIG. 7B). The otherclamp is attached to the top 752 of the other substrate of a test panel.During testing, the clamps move apart at the specified rate of extensionto pull apart the laminate. The sample specimen is pulled apart at 180degrees angle of separation between the two layers, and the peelstrength reported is the maximum tensile strength, in grams per inch,recorded during the test. Each of the peel strengths reported below isan average of five to nine tests. A suitable device for determining thepeel strength testing is a SINTECH 2 tester, available from the SintechCorporation, a business having offices at 1001 Sheldon Dr., Cary, N.C.27513; or an INSTRON Model TM, available from the Instron Corporation, abusiness having offices at 2500 Washington St., Canton, Mass. 02021; orthe Thwing-Albert Model INTELLECTII available from the Thwing-AlbertInstrument Co., a business having offices at 10960 Dutton Rd.,Philadelphia, Pa. 19154.

[0088] For a dynamic shear test, the procedure is as described aboveexcept that one clamp is attached to the top 750 of one substrate of thelaminate, and the other clamp is attached to the bottom 754 of the othersubstrate of the laminate. The shear strength reported is the maximumtensile strength, in grams per square inch, recorded during the test.Each of the shear strengths reported is an average of five to ninetests.

[0089] Molecular Weight Number Average and Weight Average)

[0090] A crystalline polypropylene was sent to American Polymer StandardCorp., a business having offices in Philadelphia, Pa., formolecular-weight determinations. The number-average and/orweight-average molecular weights were determined by American Polymerusing gel-permeation chromatography on a Waters Model No. 150gel-permeation chromatograph. The determinations were made using: four,linear, Shodex GPC gel columns; poly(styrene-divinyl benzene) copolymersas standards; trichlorobenzene as the solvent, introduced to thechromatograph at a volumetric flow rate of 1.0 milliliter per minute; anoperating temperature of 135 degrees Celsius; a sample-injection volumeof 100 microliters; an M-150C-(64/25) detector; and a GPC PRO 3.13 IBMAT data module.

EXAMPLES

[0091] Bonding strengths, i.e., dynamic shear and peel, as well asstatic peel, were determined for a blend of 20% crystallinepolypropylene and 80% APAO, and also for a control of 100% APAO. TheAPAO used was REXTAC® 2730, or RT 2730, available from HuntsmanCorporation, Salt Lake City, Utah. Crystalline polypropylene, morespecifically isotactic polypropyelen, was obtained from Sigma-Aldrich inthe form of white, spherical particles. The crystalline polypropylenewas determined to have a number-average molecular weight of about 15,000and a weight-average molecular weight of about 110,000. The procuredcrystalline polypropylene had a melting index of 1000 grams per tenminutes (at a temperature of 230 degrees Celsius and when subjected to aforce of 2.16 kg; see ASTM D 1238, which was used for thisdetermination, for additional detail on measuring the melting index).

[0092] A first series of control samples were prepared by adhesivelybonding two layers of substrate together using 100% RT 2730 melt-blownonto one of the substrates at various concentrations prior to nippingthe two substrates together with the adhesive located between the twosubstrates. A first series of test samples were prepared by adhesivelybonding two layers of substrate together using 20% crystallinepolypropylene and 80% RT 2730 melt-blown onto one of the substrates atvarious concentrations prior to nipping the two substrates together withthe adhesive located between the two substrates. A second series ofcontrol samples were prepared by adhesively bonding two layers ofsubstrate together using 100% RT 2730 applied in swirls on one of thesubstrates at various concentrations prior to nipping the two substratestogether with the adhesive located between the two substrates. A secondseries of test samples were prepared by adhesively bonding two layers ofsubstrate together using 20% crystalline polypropylene and 80% RT 2730applied in swirls on one of the substrates at various concentrationsprior to nipping the two substrates together with the adhesive locatedbetween the two substrates.

[0093] In each of the series of control samples and test samples, onesample included two necked-bonded laminate (“NBL”) substrates with theadhesive applied at 10 grams per square meter (gsm). Each NBL layer wasmade up of a polyethylene layer sandwiched between two polypropylene,spunbonded layers. A second sample in each of the series of controlsamples and test samples included two NBL substrates with the adhesiveapplied at 15 gsm. A third sample in each of the series of controlsamples and test samples included a polypropylene, spunbonded layer(“SB”) and an outercover (“OC”) comprising a polyethylene layer and apolypropylene, spunbonded layer, with the adhesive applied at 2.0 gsm inthe melt-blown samples and at 1.0 gsm in the swirl application samples.

[0094] Test results of the dynamic shear strength, dynamic peelstrength, and static peel strength for the first series of controlsamples are shown in Table 1; test results for the first series of testsamples are shown in Table 2; test results for the second series ofcontrol samples are shown in Table 3; and test results for the secondseries of test samples are shown in Table 4.

[0095] For each of the control samples and each of the test samples, thedynamic shear strength was determined as described above (i.e., oneclamp was attached to the top of one substrate of the laminate, and theother clamp was attached to the bottom of the other substrate of thelaminate, and the clamps were pulled apart at a constant rate ofextension of 300 millimeters per minute).

[0096] For each of the control samples and each of the test samples, thedynamic peel strength was determined as described above (i.e., one clampwas attached to the top of one substrate of the laminate, and the otherclamp was attached to the top of the other substrate of the laminate,and the clamps were pulled apart at a constant rate of extension of 300millimeters per minute).

[0097] For each of the control samples and each of the test samples, thestatic peel strength was determined as described above (i.e., a 500 grammass was attached to the upper edge of one of the substrates, with thetest panel suspended in an oven at a temperature of 75 degreesFahrenheit). TABLE 1 Bonding Strength of Melt-Blown Control Adhesive(100% RT 2730) Add-on/ Dynamic Shear Dynamic Peel Application (g/in²)(g/in) Static Peel NBL/NBL, 3340 740 5 min 10 gsm (NBL delaminated)(Cohesion failure) NBL/NBL, — 800 15 min 15 gsm (Cohesion failure)OC/SB,  850 310 <2 min 2.0 gsm (SB broke) (Cohesion failure)

[0098] TABLE 2 Bonding Strength of Melt-Blown Test Adhesive (20%Crystalline Polypropylene/80% RT 2730) Add-on/ Dynamic Shear DynamicPeel Application (g/in²) (g/in) Static Peel NBL/NBL, 3500 750 >48 hours10 gsm (NBL delaminated) (NBL delaminated) NBL/NBL, 3470 860 >72 hours15 gsm (NBL delaminated) (NBL delaminated) OC/SB, 1070 350 ˜10 min 2.0gsm (SB broke) (OC delaminated)

[0099] TABLE 3 Bonding Strength of Swirled Control Adhesive (100% RT2730) Add-on/ Dynamic Shear Dynamic Peel Application (g/in²) (g/in)Static Peel NBL/NBL, 2070 380 1 min 10 gsm (NBL delaminated) (Cohesionfailure) NBL/NBL, — 560 5 min 15 gsm (Cohesion failure  &  NBLdelaminated) OC/SB,  790 100 <1 min 1.0 gsm (SB broke) (Cohesionfailure)

[0100] TABLE 4 Bonding Strength of Swirled Test Adhesive (20%Crystalline Polypropylene/80% RT 2730) Add-on/ Dynamic Shear DynamicPeel Application (g/in²) (g/in) Static Peel NBL/NBL, 3590 870 ˜24 hours10 gsm (NBL delaminated) (NBL delaminated) NBL/NBL, — 990 >72 hours 15gsm (NBL delaminated) OC/SB,  880 300 ˜10 min 1.0 gsm (SB broke) (OCdelaminated)

[0101] As can be seen by comparing Table 1 to Table 2, and Table 3 toTable 4, the bonding strength of the blend of crystalline polypropyleneand RT 2730 is considerably greater than the bonding strength of the RT2730 alone, in terms of dynamic shear strength, dynamic peel strength,and static peel strength, in each of the samples. The improved bondingstrength is particularly noticeable in the swirl applications.

[0102] Another observation that is apparent from Tables 2 and 4 is thatthe dynamic shear bond strength in laminates bonded with the blend ofcrystalline polypropylene and RT 2730 is greater than the dynamic shearmaterial strength of the substrates. More specifically, the testsresulted in either delamination of the NBL or breakage of the SB, ratherthan cohesion failure. Similarly, Tables 2 and 4 also show that thestatic peel bond strength in laminates bonded with the blend ofcrystalline polypropylene and RT 2730 is greater than the static peelmaterial strength of the substrates. More specifically, the testsresulted in delamination of either the NBL or the OC, rather thancohesion failure.

[0103] The remarkable difference between bonding strength of the blendand RT 2730 alone may be attributed to forming a crystal domain of thecrystalline polypropylene. The crystal domain of the crystallinepolypropylene generates physical cross-linking in the matrix of theAPAO. The remarkably improved performance of bonding strength of theblend in the swirl application compared to melt-blown may be due to alarger ratio of mass of blend to bonding area in the swirl applicationthan that of melt-blown, thus resulting in more crystallization.

[0104] It will be appreciated that details of the foregoing embodiments,given for purposes of illustration, are not to be construed as limitingthe scope of this invention. Although only a few exemplary embodimentsof this invention have been described in detail above, those skilled inthe art will readily appreciate that many modifications are possible inthe exemplary embodiments without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention, which is defined in the following claims and all equivalentsthereto. Further, it is recognized that many embodiments may beconceived that do not achieve all of the advantages of some embodiments,particularly of the preferred embodiments, yet the absence of aparticular advantage shall not be construed to necessarily mean thatsuch an embodiment is outside the scope of the present invention.

What is claimed is:
 1. A hot-melt, pressure-sensitive adhesivecomposition, comprising: between about 70% and about 90% amorphouspolyalphaolefin including butene-1 copolymer; and between about 10% andabout 30% crystalline polypropylene having a degree of crystallinity ofat least about 40%.
 2. The adhesive composition of claim 1, comprisingbetween about 73% and about 87% of the amorphous polyalphaolefin, andbetween about 13% and about 27% of the crystalline polypropylene.
 3. Theadhesive composition of claim 1, comprising between about 75% and about85% of the amorphous polyalphaolefin, and between about 15% and about25% of the crystalline polypropylene.
 4. The adhesive composition ofclaim 1, wherein the degree of crystallinity of the crystallinepolypropylene is at least about 60%.
 5. The adhesive composition ofclaim 1, wherein the degree of crystallinity of the crystallinepolypropylene is at least about 80%.
 6. The adhesive composition ofclaim 1, wherein the amorphous polyalphaolefin has a number-averagemolecular weight between about 5,000 and about 30,000.
 7. The adhesivecomposition of claim 1, wherein the amorphous polyalphaolefin has aweight-average molecular weight between about 20,000 and about 60,000.8. The adhesive composition of claim 1, wherein the crystallinepolypropylene has a number-average molecular weight between about 3,000and about 200,000.
 9. The adhesive composition of claim 1, wherein thecrystalline polypropylene has a number-average molecular weight betweenabout 10,000 and about 100,000.
 10. The adhesive composition of claim 1,wherein the adhesive composition has a melt index between about 200 andabout 2000 grams per 10 minutes.
 11. The adhesive composition of claim1, wherein the adhesive composition has a melt index between about 400and about 1800 grams per 10 minutes.
 12. The adhesive composition ofclaim 1, wherein the adhesive composition has a melt index between about500 and about 1500 grams per 10 minutes.
 13. The adhesive composition ofclaim 1, wherein the butene-1 copolymer comprises between about 25% andabout 65% by weight butene-1, and a balance of a comonomer selected fromthe group consisting of ethylene, propylene, and combinations thereof.14. The adhesive composition of claim 1, wherein the butene-1 copolymercomprises between about 30% and about 55% by weight butene-1, and abalance of a comonomer selected from the group consisting of ethylene,propylene, and combinations thereof.
 15. The adhesive composition ofclaim 1, wherein the crystalline polypropylene comprises at least one ofthe group consisting of isotactic polypropylene, syndiotacticpolypropylene, and combinations thereof.
 16. A laminated structurecomprising: a first substrate; a second substrate; and a hot-melt,pressure-sensitive adhesive composition bonding the first substrate andthe second substrate to one another, wherein the adhesive compositionincludes an amorphous polyalphaolefin and a crystalline polypropylenehaving a degree of crystallinity of at least about 40%.
 17. Thelaminated structure of claim 16, comprising between about 70% and about90% of the amorphous polyalphaolefin, and between about 10% and about30% of the crystalline polypropylene.
 18. The laminated structure ofclaim 16, comprising between about 75% and about 85% of the amorphouspolyalphaolefin, and between about 15% and about 25% of the crystallinepolypropylene.
 19. The laminated structure of claim 16, wherein thedegree of crystallinity of the crystalline polypropylene is at leastabout 60%.
 20. The laminated structure of claim 16, wherein the degreeof crystallinity of the crystalline polypropylene is at least about 80%.21. The laminated structure of claim 16, wherein the amorphouspolyalphaolefin has a weight-average molecular weight between about20,000 and about 60,000.
 22. The laminated structure of claim 16,wherein the amorphous polyalphaolefin has a weight-average molecularweight between about 25,000 and about 50,000.
 23. The laminatedstructure of claim 16, wherein the crystalline polypropylene has anumber-average molecular weight between about 3,000 and about 200,000.24. The laminated structure of claim 16, wherein the crystallinepolypropylene has a number-average molecular weight between about 10,000and about 100,000.
 25. The laminated structure of claim 16, wherein theamorphous polyalphaolefin comprises a butene-1 copolymer with ethylene.26. The laminated structure of claim 16, wherein the amorphouspolyalphaolefin comprises a butene-1 copolymer with propylene.
 27. Thelaminated structure of claim 16, wherein the amorphous polyalphaolefincomprises an ethylene-propylene copolymer having up to 80% ethylene. 28.The laminated structure of claim 16, wherein the amorphouspolyalphaolefin comprises a butene-1 terpolymer with ethylene andpropylene.
 29. The laminated structure of claim 16, wherein thecrystalline polypropylene comprises at least one of the group consistingof isotactic polypropylene, syndiotactic polypropylene, and combinationsthereof.
 30. The laminated structure of claim 16, wherein the first andsecond substrates are each part of a single substrate.
 31. The laminatedstructure of claim 16, wherein each of the first and second substratesis selected from the group consisting of: nonwoven material, wovenmaterial, and film.
 32. The laminated structure of claim 16, wherein atleast one of the first and second substrates comprises at least one ofthe group consisting of cellulosic material, thermoplastic material, andcombinations thereof.
 33. The laminated structure of claim 16, whereinat least one of the first and second substrates comprises at least oneof the group consisting of a necked-bonded laminate, a polypropylenespunbonded layer, and a polyethylene layer in combination with apolypropylene spunbonded layer.
 34. The laminated structure of claim 16,wherein the first and second substrates each comprise a neck-bondedlaminate.
 35. The laminated structure of claim 16, wherein the firstsubstrate comprises a film and the second substrate comprises a spunbondweb.
 36. The laminated structure of claim 16, wherein the adhesivecomposition is melt-blown onto at least one of the first and secondsubstrates.
 37. The laminated structure of claim 16, wherein theadhesive composition is applied to at least one of the first and secondsubstrates in a swirl pattern.
 38. The laminated structure of claim 16,wherein the adhesive composition is applied to at least one of the firstand second substrates in a concentration of between about 1 gram persquare meter and about 50 grams per square meter.
 39. The laminatedstructure of claim 16, wherein the adhesive composition is applied to atleast one of the first and second substrates in a concentration ofbetween about 5 grams per square meter and about 20 grams per squaremeter.
 40. The laminated structure of claim 16, wherein the laminatedstructure has a dynamic shear bond strength greater than a dynamic shearmaterial strength.
 41. The laminated structure of claim 16, wherein thelaminated structure has a static peel bond strength greater than astatic peel material strength.
 42. An absorbent article comprising: afirst substrate; a second substrate; and a hot-melt, pressure-sensitiveadhesive composition bonding the first substrate and the secondsubstrate to one another, wherein the adhesive composition includesbetween about 70% and about 90% amorphous polyalphaolefin includingbutene-1 copolymer, and between about 10% and about 30% crystallinepolypropylene having a degree of crystallinity of at least about 40%.43. The absorbent article of claim 42, wherein the butene-1 copolymercomprises between about 20% and about 65% by weight butene-1, and abalance of a comonomer selected from the group consisting of ethylene,propylene, and combinations thereof.
 44. The absorbent article of claim42, wherein the butene-1 copolymer comprises between about 30% and about55% by weight butene-1, and a balance of a comonomer selected from thegroup consisting of ethylene, propylene, and combinations thereof. 45.The absorbent article of claim 42, wherein the crystalline polypropylenecomprises at least one of the group consisting of isotacticpolypropylene, syndiotactic polypropylene, and combinations thereof. 46.The absorbent article of claim 42, wherein at least one of the first andsecond substrates comprises at least one of the group consisting of anecked-bonded laminate, a polypropylene spunbonded layer, and apolyethylene layer in combination with a polypropylene spunbonded layer.47. The absorbent article of claim 42, comprising a diaper.
 48. Theabsorbent article of claim 42, comprising swim wear.
 49. The absorbentarticle of claim 42, comprising child training pants.
 50. The absorbentarticle of claim 42, comprising an adult incontinence garment.
 51. Theabsorbent article of claim 42, comprising a feminine care product. 52.The absorbent article of claim 42, comprising a medical garment.